The edition of Plato's complete works published in Geneva in 1578 by
printer Henri Estienne (1528-1598), better known under his latin name Stephanus,
who was also a famous scholar of the time and who had himself established
the Greek text of Plato he was publishing, was not the first printed edition
of Plato's dialogues. It had been preceded by that of Aldus Manucius, published
in Venice in 1513 in two volumes, and by the one published in 1534 in Basel
by Valder, with the help of Simon Grynaeus and John Oporinus. If it deserves
special attention, it is because it remained for several centuries the reference
edition and because it still provides today the basis of the universally
accepted way of quoting Plato. It included, in three volumes, all the then
extant works attributeds to Plato, that is 42 titles, distributed as follows:

It included, spread over two columns per page, the Greek text established
by Henri Estienne himself and a Latin translation by Jean de Serre (Serranus
in Latin).

The picture below shows the cover page of this edition.

The
picture below shows the title page of volume two of this edition.

The pictures below show pages 514 to 518 of volume two, which include the
beginning of book VII of the Republic, that is, the allegory of
the cave. It can be seen that the Greek text is in the second column of odd
pages (column on the right of the page) and the first column of even pages
(column on the left of the page), that is, always in the inner column, closer
to the binding: it is the text that makes up the main body of the book and
can be read continuously from page to page.The Latin translation wraps it
from the outside, itself supplemented by notes in the margins. One may notice
on each page, between the column with the Greek text and that with the Latin
translation, letters A, B, C, D and E located at regular intervals, every
tenth line or so of the Greek text (intervals between lines of the Greek
text are not the same as those between lines of the Latin translation, the
later being more compact), starting with A on the first line of the page
and dividing the page into five sections of about ten lines of Greek text
each; but it can be seen that the letters don't always fall exactly in front
of a line of the Greek text and so, for instance, the E on page 515 falls
between two lines of the Greek text, section D of that page includes 11 lines
and section E only 8. It can also be seen that, in order to provide on the
same page both a portion of Greek text and its translation in Latin, not
only the intervals between lines of the Latin translation had to be shorter
than the one between lines of the Greek text, as has already been said, but
on top of that, on some pages, tha Latin text at the bottom of the page spreads
over the two columns below the end of the Greek text on that page, reducing
the number of lines of Greek text in section E to the point where, in some
cases, it may end up with only one or two lines (two lines for instance on
page 517). Besides, additional numbered notes can be found at the end of
each dialogue or book (in the case of Republic and Laws,
what we now call "books" in those works is being called "dialogues" by Henri
Estienne, as can be seen on page 514 from the heading Politeiôn
dialogos hebdomos, meaning "seventh dialogue of the Republic"),
which may spread over several pages or sections of pages, so that the ensuing
dialogue or book doesn't always start on top of a new page and may, as a
result, end up with a reduced number of sections, not ending with section
E. Such a situation can be seen on page 514, whose top is occupied by the
end of the notes relating to the previous "dialogue", in that case, book
VI of the Republic. Beside, section A of the first page of a dialogue,
even though it includes ten lines, holds less text than normal sections because
of the space occupied by the larger adorned initial letter of the dialogue.
Finally, as can be expected, even though no exemple of it is provided here,
the end of a dialogue or book doesn't usually fall exactly at the end of
a page, so that, here again, the last page doesn't always include all five
sections A to E.

Those remarks are important because, as I said at the beginning of this
page, this edition still serves today as the basis for the universally agreed
upon way of quoting Plato, using the page number in the Stephanus edition,
followed by the letter identifying the section in the page and the line number
within that section from that letter. They help explain some specific features
of this numbering (discontinuity within page numbers between dialogues or
books within dialogues, missing letters on certain pages, varying size of
sections in number of lines, etc.) A complete description of this way of
quoting Plato along with a more detailed description of the contents of each
volume, includint the start and end page number of each dialogue and book
(for Republicand Laws) can be found in the
page of this site answering question 7 of the frequently asked questions,
"Quoting Plato".